Process for treating liquid containing tar acid



J. A. SHAW Sept. 26, 1933.

PROCESS FOR TREATING LIQUID CONTAINING TAR ACID Original Filed Nov. 2, 1927 INVENTOR. vbsgofr AIS/7cm B Y x Patented Sept, 26, 1933 PROCESS FOR TREATING LIQUID coNraiNiNc ran AGED JosephAf. Shaw, Pittsburgh, Pa, assignor to The Koppers' (Jernpany of Delaware, a corporation of Delaware 5 Claims. (Cl. 260-454) I invention relates to the treatment of liq:

uids' containing tar acids,such as, phenol, cresol and'analogous impuritiesh I My invention relates broadly to the removal of B. tar acids from any liquid that may contain them,

butit' has particular application to the treatment of condensatesirom gas derived from the various systems of coal carbonization and gasification,

for example, gas liquor. j' "i h This application is a division of myapplication Serial No. 230,570, filed November2, 1927.

An object of the present invention is 'to'pro vide a process of and apparatus for accomplishing the removal of tar acids from liquid containing them.

more complete removal of tar acids from liquid than has been possible by means of, prior 'proc essesland apparatus. i r j Gasliquor is produced incooling and condensing. coalv gas as produced in by-product coke ovens, gas. retorts and the like. [This liquorconsection? and. a lime leg. The "free ammonia is ,d rivenlofi by steam in the free ammonia still, and the partially distilled. liquor enters thelime ,leg, where it ismixed with milkof lime. The mixture. of. milk oflime and liquor is then'treated with steam in the fixed ammonia still where'the fixed ammonia of the liquor is decomposed and the ammonia driven ed in vapor form.

1 Thezefiluent or waste liquor from the fixed am- ;rnonia. still containslprinc'ipally various calcium salts formed in the decompositionoi fixed ammonia,..and is disposedoi by draining it into a sewer or stream, or in any other feasiblemanner. 1

Tar acids contained in the gas liquor, if not volatilized and removed'in the free ammonia still, a'recarried downwith the gas liquo'r descending the still, and react with milk of lime' to form-calcium compounds. Such compounds are not volatile, and consequently escape from the tiomismakingitmoreand more difficult for gas A further' object of 'myi'nvention is to provide a process of and apparatus for accomplishing manufacturers or others todispose'of ammonia still eiiluent containing tar acids by simply drain ing it into a sewer or stream. In the sterilization of Water for drinking purposes by means of ch10 rine or'chlorine compounds, if tar acids are prescut, chlorphenolsand analogous-substances are produced that are capable ofimpa-rting a dis-' agreeable taste and odor tolarge amountsof water and which are on this account highly noxions in character. I f 5 It is thus desirable to accomplish substantially complete removal of" taracids eitherfrom'the gas liquor itself or from theefflu ent or waste liquor, prior to disposal of the latter;

According to my invention, I provide for the substantially complete removal of tar acids from the gas liquor upon or beforedistillation of free ammonia therefrom.

I have found that substantially complete elimination of tar acids from gas liquor-"may beac-- complisned by heating the liquor to just below "its boiling point and holding, it at this temperai from, preferably with an alkali, for example a solution oi sodium hydroxide. The gas is then recirculated for further use.

With respect to gas liquor, the process of my, 5 invention may be performed in several ways that are broadly divisible according towhether the gasliquor is treated before or afterdistillation of its fixed ammonia content. In either case, it is desirableto insure that substantially all of the tar acids present in -the liquor are brought to the point of removal in, order to-prevent their escape intoother parts of the system, entrapment in the waste liquor, and the like.

The gasliquor may betreated for removal-of tar acids prior toiintroduction into the ammonia still if so desired, but in this instance the removal oftar acids accomplishedjin conjunction with the distillation offreeammonia.

' ,Moreover, my process may be variously per- .formed in this respect accordingto whether it is cially designed for this purpose, and with respect to various other considerations. 7'

'In the former case, i. e., when it is desired to utilize an existing. ammonia still of the usual type, it is desirable'to provide for the substan- ,tially complete removalof tar'acids from thelli) gas liquor in the ammonia still itself, but also to prevent escape of these impurities into certain other parts of the system for example, the ammonia saturator, the final cooler, or the like. In my process this end is attained without modification of existing structure except insofar as additional and separate apparatus may be required for the treatment of the tar acids.

In order that my invention may be clearly set forth and understood, I now describe, with reference to the accompanying drawing, a particular manner in which my invention may be embodied and performed. In this drawing,

The single figure is an elevational view, partially in section, of apparatus for distilling gasv liquor and for removing and recovering tar acids therefrom, parts being broken away.

Referring to the figure, the distillation of gas liquor or other ammoniacal liquor containing tar acids is conducted in an ammonia still unit 1 of the usual type. This unit is comprised of a free ammonia still 2 and a fixed ammonia still 3. The stills 2 and 3 are constituted of a plurality of superimposed bell-and-tray sections, the bell-and-tray sections of the free ammonia still 2 being supported upon a large section or lime-leg 4 that is adapted to contain milk of lime. v

The liquor is admitted to the still 2 through an inlet conduit 5, the rate of flow being regulated by a valve 6. 'The gas liquor passes downward through the free ammonia still'2, traverses the lime leg 4 and passes through a conduit 7 into the fixed ammonia still 3. The limed liquor now passes down through the fixed ammonia still 3 and the effluent escapes through a drain 8.

Steam and milk of lime are admitted as necessary. During the progress of the gas liquor through the free ammonia still 2, the free ammonia is distilled off, escaping from the still 2 through a distillate pipe 9. The gas liquor, less its free ammonia content, now enters the lime leg 4 and is mixed with milk of lime, whereby the fixed ammonia is decomposed into free ammonia that is then distilled off in the still 3. The volatilized ammonia then passes through a pipe 10,

through the still 2 and escapes through the pipe 9.

In the present instance, the distillation of the gas liquor is conducted in such manner as to liberate substantially all of the tar acids there- V .monia and to prevent undue losses due to latent from prior to contact of the liquor with milk of lime. This may be accomplished by maintaining the temperature in the top section of the free ammonia still 2- at a relatively high temperature, preferably about the boiling point of the liquor. .As in other cases where steam distillation is employed, the volume of steam and gases may be a considerable factor in the removal of the tar acids. It is in this instance important to substantially completelyremove tar acids from the gas liquor prior to contact with milk of lime in the lime leg 4, for the reason that these impurities, upon contactwith lime, are rendered nonvolatile and will accordingly be carried out in this tar acids therefrom.

The ammonia gas, HzS, HCN, CO2, steam, and volatilized tar acids pass through the pipe 9 into a dephlegmator 11 where they are cooled to below the volatilization point of the tar acids.

The re maining ammoniacal vapors pass through a line 12 to a condenser (not shown), or into the gas main at a point just prior to the entry of the gas into the ammonia saturator.

The dephlegmator 11 is maintained at such temperature as will effect a condensation of the tar acids but without condensing any more ammonia than is absolutely necessary. The actual temperature employed will vary somewhat and no specific temperature will apply under all conditions. Ordinarily, it is desirable to effect a condensation of only so much water as will serve to remove substantially all of the tar acids from the vapors. This amount will depend somewhat upon the construction of the dephlegmator. A temperature of about 60 C. has been found proper under certain conditions.

The liquid condensing in the dephlegmator 11 and containing substantially all of the tar acids originally present in the gas liquor runs by gravity through a pipe 13, into a heater 14, where it is heated, preferably indirectly, to a temperature justbelow its boiling point, and then enters a stripping tower 15 through a plurality of sprays 16 that serve to distribute the liquid evenly over the upper surface of a suitable'quantity of contact material 17 within the tower 15. The contact material '17 may be any suitable material, such as coke, tile or the like, that is adapted to effect intimate contact between streams of liquid and gas flowing therethrough. The tower 15 is preferablyinsulated to prevent undue cooling of the liquid and gas within the same.

During the passage of the hot liquid downward through the contact material 17, it is exposed to a rising current of an inert gas, such as air which is substantially inert with respect to tar acids. By reason of the high temperature of the liquid and the scrubbing action of the gas, the tar acids present inthe liquid are volatilized and carried oif by the gas escaping with the gas from the tower 15 through a pipe 18. The liquid as free from tar acids as is necessary collects in the bottom of the tower 15 and is withdrawn through a drain pipe 19. This liquid, if it contains any conids siderable quantities of ammonia, may be redistilled, but this is usually unnecessary. For

this purpose the pipe 19 may be connected to the still 2 and provided with a valve 30, a pump 31 and a valve 32 for controlling the flow of liquid from the tower 15 to the still 2.

In order to preventunnecessary loss of amheat of vaporization, it is desirable to employ the gas used for removing tar acids from the liquid from the dephlegmator 11 in a closed cycle com- 4 prising recirculation through the tower 15 and a washer 20, wherein the gas is treated for re- To describe the gas cycle in more detail, the gas enters the tower 15 at the bottom thereof through a pipe 21 under action of a blower 22 and passes upward through the tower 15, emerging from the latter at the top thereof and passing through conduit 18' into the lower part of the washer 20.

In the present instance a Feld washer is employed for treating the gas. This washer 20 is of the usual construction and is provided with heating means, for example, a steam line 23.

The washer 20 is supplied with a solution of caustic soda (NaOH) from a suitable reservoir 24 through a sealed pipe 25, wherein is situated a sight-feed 26 to facilitate regulation of flow. The gas and caustic solution pass through the washer 20 in counter-current and tar acids present'in the gas are absorbed by the caustic the boiling point of the liquor, and is consequently saturated with water vapor, being thus in effect a mixture of gas and steam.

The rate of flow of the solution is further regulated according to the tar acid content of the gas emerging from the washer 20, which should be substantially nil.)

This phenol-free gas passes out of the washer 20 through a pipe 28' and is drawn into the blower 22, whence it is forced through pipe 21 into the I tower 15qfor treatment of further quantities of substantially no tar acids are carried into the main gas stream or the condenser nor does the efiiuent liquorfrom the fixed ammonia still 3 contain any substantial amount of tar acids. Thus the object of the present invention is accornplished. v While Ihave described my invention hereinabove withrespect to certain specific examples, it is not limited to such specific illustrative methods or apparatus but maybe variously performed Within the scope of the following claims.

I claim as my invention:

1. The process of treating'gas liquor which comprises vdistilling said liquor, cooling thereby liberated vapors of ammonia and tar acid to such extent as to condense tar acid therefrom, and subjecting the condensate thereby obtained to contact with a substantially inert gas at a temperature not substantially below its boiling point for the removal of tar acid therefrom. l

2. The process of treating gas liquor which comprises distilling said liquor cooling thereby liberated vapors of ammonia and tar acid to such extent as to condense tar acid therefrom, subjecting the condensate thereby'obtained to contact with a substantially inert gas at a temperaturenot substantially below its boiling point for the removal of tar acid therefrom, removing the thereby tar acid laden gas from said liquid, subjecting it to contact with an agent eifective to remove tar acid therefrom maintained at a temperature not lower than that of said condensate, and recirculating said gas for further contact with said condensate.

3. The process of treating gas liquor which comprises distilling said liquor, cooling thereby liberated vapors of ammonia and tar acid said vapors to such extent as to separate therefrom a condensate containing tar acid, and subjecting said condensate to contact with a substantially inert gas recirculated through a cycle comprising said contact stage andan absorption stage wherein said gas is brought into contact with an agent having absorbent properties with respect to tar acid but not with respect to ammonia.

4. The process of treating gas liquor which comprises distilling said liquor, cooling thereby liberated vapors of ammonia and tar acid said vapors to such extent as to separate therefrom a condensate containing tar acid, subjecting said condensate to contact with a substantially inert gas recirculated through a cycle comprising said contact. stage and an absorption stage wherein said gas is brought into contact with an agent having absorbent properties with respect to tar I acid but not with respect to ammonia, and finally a gas and liquid contact device lying in the path, of condensate liquor leaving said cooler, a second gas and liquid contact device adapted to receive a tar acid absorbent liquid, and means for recirculating a substantially inert gas through a cycle comprising said gas and liquid contact devices.

JOSEPH A. SHAW. 

